Our hominid ancestors Homo erectus turned rocks like this into complex tools nearly two million years ago...hundreds of thousands years earlier than previously thought. The new find helps fill in some crucial blanks in our evolutionary history.

Many animals have come up with the basics of tool use, but it was Homo erectus that first began refining the very simple stone tools used by its evolutionary ancestors into move innovative designs. Previously, hominids had only used stones as tools for chipping, not doing much more than smashing their tools against other surfaces. Homo erectus, on the other hand, figured out how to sharpen specific edges of their stones, forming hand axes, picks, and other tools. Lehman College paleoanthropologist Eric Delson explains the capabilities of these tools:

"You could whack away at a joint and dislodge the shoulder from the arm, leg or hip. The tools allowed you to cut open and dismember an animal to eat it."

According to a new find in what is now West Turkana, Kenya, these ancient hominids had already developed these tools - known as Acheulian technology - by as far back as 1.8 million years ago. That pushes back the invention of the technology by a good 300,000 years, and it also pushes back the development of the skills needed to create such tools. Acheulian technology required Homo erectus to have nimble, dexterous control of their hands, and it also required a fairly complex understanding of how refining the stones now could be helpful in the future. That sort of long-term planning was a huge evolutionary innovation for Homo erectus.

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The previous record holders for the first Acheulian tools were found in Konso, Ethiopia, dating back about 1.4 million years, and in India, which could date from anywhere between 1.5 and 1 million years ago. The discovery of Acheulian tools in East Africa dating back 1.8 million years is particularly intriguing, because it might help us figure out just where Homo erectus originated. An erectus site from roughly the same period has also been found in the modern-day country Georgia, which has led to some speculation that the species evolved in Asia, not Africa.

We do know that the Homo erectus site in Dmanisi, Georgia did not possess Acheulian technology - they only had the simple chopping tools that their counterparts in East Africa had managed to render obsolete. There are a number of ways to explain this discrepancy - perhaps Homo erectus split into Asian and African groups before the development of Acheulian technology, or maybe Homo erectus somehow "lost" the technology while moving from Africa to Asia. The latter would suggest an African origin for the species, while the former leaves it up in the air.

One reasonable hypothesis is that Acheulian technology was necessitated by changing climatic conditions in East Africa about 2 to 1.5 million years ago. Monsoon rain patterns shifted during that period, causing the African savanna to spread out and conditions to become generally drier. This would mean a loss of some of the lusher food resources, which would make the presence of more powerful tools a huge boon to Homo erectus. It's possible that ancient Georgia did not carry the same sorts of environmental pressures, and so the species could safely "lose" the knowledge of Acheulian technology without dying out.